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06-25-2024

Hydrothermal vents could support life on Jupiter's moons

We’ve all seen the surreal footage of hydrothermal vents on the frigid ocean floor, spewing black plumes of super-hot water and teeming with life.

A new study suggests that lower-temperature vents, common across Earth’s seafloor, may create life-supporting conditions on “ocean worlds” in our solar system.

What are ocean worlds?

Ocean worlds are planets and moons that have, or had, liquid oceans. Often, these oceans lie beneath an icy shell or within their rocky interiors.

In our solar system, several of Jupiter’s and Saturn’s moons are ocean worlds. Their existence has inspired academic studies, spacecraft missions, and even popular movies like The Europa Report.

Heat and hydrothermal circulation

Research suggests that some ocean worlds generate enough internal heat to drive hydrothermal circulation under their seafloors. This heat is produced by radioactive decay and tidal forces.

On Earth’s seafloor, hydrothermal systems were discovered in the 1970s, revealing ecosystems around vents that discharge heat, particles, and chemicals.

Simulating hydrothermal life on Earth

In this new study, researchers from the University of California, Santa Cruz used a complex computer model based on Earth’s hydrothermal circulation.

By altering variables such as gravity, heat, rock properties, and fluid-circulation depth, they found that hydrothermal vents could be sustained under a wide range of conditions.

If these flows occur on ocean worlds like Jupiter’s moon Europa, the chances of life existing there increase.

“This study suggests that low temperature hydrothermal systems could have been sustained on ocean worlds beyond Earth over timescales comparable to that required for life to take hold on Earth,” said Andrew Fisher, the study’s lead author and a distinguished professor of Earth and planetary sciences at UC Santa Cruz.

Earth’s cooling system

The seawater-circulation system that the team modeled is based on a 3.5 million-year-old seafloor in the northwestern Pacific Ocean.

There, cool bottom water flows through an extinct volcano, travels underground for about 30 miles, and emerges warmer with different chemistry.

“The water gathers heat as it flows and comes out warmer than when it flowed in, and with very different chemistry,” explained PhD candidate Kristin Dickerson, the second author of the paper.

This flow is driven by buoyancy, as water becomes less dense when heated and more dense when cooled

The system, termed a “hydrothermal siphon,” continues as long as heat is supplied and the rock allows fluid circulation.

Potential for life on ocean worlds

High-temperature vent systems on Earth are driven mainly by volcanic activity, but a larger volume of fluid flows at lower temperatures, driven by Earth’s “background” cooling.

This low-temperature venting discharges as much water as all the rivers and streams on Earth combined, accounting for about a quarter of Earth’s heat loss.

Previous studies of hydrothermal circulation on Europa and Saturn’s moon Enceladus focused on high-temperature fluids.

However, lower-temperature flows are just as likely. “Lower-temperature flows are at least as likely to occur, if not more likely,” noted study co-author Donna Blackman, an EPS researcher.

Longevity of hydrothermal systems

One exciting result from the computer simulations showed that under very low gravity – like that on Enceladus – circulation can continue with low to moderate temperatures for millions or billions of years.

This finding helps explain how small ocean worlds can have long-lived fluid-circulation systems below their seafloors, even with limited heating.

The future of hydrothermal research

Planetary scientists are looking to satellite mission observations to determine the conditions on ocean worlds. The authors of the study plan to attend the launch of the Europa Clipper spacecraft later this fall, a mission aimed at exploring these fascinating environments.

Directly observing the seafloors of ocean worlds for active hydrothermal systems remains challenging due to their distance from Earth and physical characteristics. Thus, it is essential to maximize available data, much of it collected remotely, and leverage decades of detailed studies of Earth’s analog systems.

This study opens new possibilities for understanding life-supporting conditions on other planets and moons, suggesting that the potential for life beyond Earth is greater than we once thought.

The study is published in the journal  Journal of Geophysical Research: Planets.

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